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Art. XXL — Account of cm Improved Hygrometer. By JoH^ 
Livingstone, M. D. of Canton 
Having observed in the process of making ice, that the 
power of tile sulphuric acid was remarkably equable from the 
point of its highest concentration till it had formed ice twelve 
or fifteen times, I was led to entertain the expectation, that it 
might be found to act with sufficient uniformity in a more ad- 
vanced state of saturation. As the trials which I made were 
highly satisfactory, I shall briefly describe my method of con- 
structing a Hygrometer upon this principle. 
In the scales commonly used as a hydrostatic balance, I 
placed a small porcelain disli three inches in diameter, containing* 
SI grains of very pure sulphuric acid, of the specific gravity 
1.845, and 29 grains of distilled water. Having exposed it to 
the greatest degree of artiflcial moisture, I found that it gained 
50 grains in 24 hours. When it was afterwards placed for one 
night in a platina dish over concentrated sulphuric acid, and un- 
der the receiver of the ice machine, its weight was reduced to 50 
grains without exhausting any of the air. 
Half a grain made the edge of the scale of this balance de- 
scribe an arch, exceeding an inch both above and below the le- 
vel. This space I divided into ten equal parts both above and 
below, or the grain into 20 parts, whiclq multiplied by the 50 
grains, gave me a scale of 1000. 
I have used this instrument, inclosed in a glass cover, but 
sufficiently open below to admit the air freely, for nearly six 
montlis ; and, from a careful comparison mth other hygrometers, 
I am persuaded it is more accurate than any now in use, though, 
in its present state, it is less sensible than KateVs. 
It has frequently approached in the natural atmosphere, with- 
in a few divisions of the point of greatest humidity, and also 
within 143 of that of greatest dryness. Considering this range, 
* We have been favoured with this extract of a letter from Dr Livingstone, 
by a gentleman who has seen the instrument which it describes. From the same 
quarter we are led to expect a detailed account of Dr Livingstone’s meteorological 
observations in China, which we have reason to' believe will prove in the highestr 
degree interesting.— E d, 
